WO 2009/122137 describes a system for selecting an initial profile to use within a DSL access network circa the priority date of March 2008. The invention particularly concerned the selection of a suitable profile for a line being moved into a rate adaptive mode of operation having previously been operated in a non-DSL mode (e.g. a Plain Old Telephone Services (POTS) mode) or in a fixed rate mode (i.e. a non-rate adaptive mode) in which profiles are generally not used in the same way as in a rate adaptive mode. In the access network described in WO 2009/122137, the rate adaptive mode of operation employed ADSL (including ADSL1, ADSL2 and ADSL2+ as specified in ITU standards G.992.1, G.992.3 and G.992.5 respectively), as did the non-rate adaptive broadband modes (although only ADSL1 and ADSL2). Moreover, when a user upgraded service from a POTS or non-rate adaptive service to a rate-adaptive service, the same copper connection was used for the new service as for the old service.
Since that time BT's access network (and many other access networks throughout the world) has (have) evolved to deploy fiber into the network between local exchange buildings and VDSL2-enabled street cabinets such that VDSL2 (G.993.2) is now used for many connections providing connection rates of (typically) up to 70 Mbits/second in the downstream direction (from cabinet to user premises) and up to 20 Mbits/second in the upstream direction (from user premises to cabinet). Moreover, it is anticipated that the next main evolution of the copper access network in the UK (and similarly in many other countries) will be the deployment of further optic fiber connections to DSLAM's located in Distribution Points (DP's) even closer to end user premises than street cabinets and employing G.Fast modems in both a DSLAM located in the drop point and in a corresponding Customer Premises Equipment (CPE) modem located in the customer's premises.
When a user upgrades to a VDSL2 service from another service (e.g. a POTS service, or an ADSL fixed rate or rate-adaptive mode service) the copper connection will typically be fundamentally different to that used in the previous service. This is because in the VDSL2 service the connection between the CPE and the Exchange now comprises a copper connection between the cabinet and the CPE modem and a fiber-optic connection between the cabinet and the exchange whereas previously there was a single copper connection between the CPE modem and the exchange. Similarly, for a user upgrading to a G.Fast connection in the future, the new connection will comprise a copper connection between the Distribution Point (DP) and the CPE modem with a fiber-optic connection between the DP and the Exchange whereas previously the user would have had either a copper connection between the CPE modem and the exchange (e.g. for ADSL and POTS services) or (for VDSL2 services) a copper connection between the CPE modem and the cabinet and a fiber optic connection between the cabinet and the exchange.
Furthermore, as the access networks have evolved, so have the DSL protocols employed in the newer better services. This has provided more control options for operators to use in order to control the behavior of a connection. In addition, operators have started to control connections by setting a cap on the maximum rate at which a particular connection can synchronize (below the maximum rate available for a particular DSL protocol being employed—e.g. 100 Mbits/s for VDSL2 connections using up to approximately 17 Mhz). These developments have led to a large increase in the number of protocols used in controlling DSL connections compared to the access network described in WO 2009/122137.
Because of these developments the approach described in WO 2009/122137 is no longer optimal for new VDSL2 connections, both because the performance of the copper connection has changed (i.e. reduction in length) and the transmission system has an increase in spectrum from 2.2 MHz to 17.6 MHz such that measurements associated with the old service will have less bearing on the likely behavior of the new service (because the physical copper connection is very different in the new service compared to the previous services) and because there are now so many very different profiles in use, a simple hard-coded rule of thumb type approach is less feasible. For these reasons, many access networks simply use a default initial profile when initializing a new service and then allow Dynamic Line Management (DLM) to modify the profile employed for a new connection until a more appropriate profile is finally selected after several iterations of the DLM process.
The use of higher frequencies have also made factors such as method of installation and local noise factors far more important when trying to select an initial profile.